Can't answer your first question, but on your second one, I'd move Nikko Blue somewhere where it does not get any hot afternoon sun. Having tried to grow it in afternoon sun, I can assure you that it will never adjust to the heat/sun and might not even survive in such a situation if your summer sun is as hot as it is here in Kansas.

Kate

I've had Nikkos bloom when they shouldn't have, so I assume they may have bloomed on new wood.

I don't know where you are in Z5, but where I am (North East), the incredibly hot summer with spring's lack of decent rain has caused all of my hydrangea to droop every afternoon. They'll only get some supplemental watering once or twice a week.